1. Field of the Invention
The present invention relates to an apparatus and a method for subjecting semiconductor devices to plasma treatment and, more specifically, to such an apparatus and a method used to subject semiconductor devices to plasma treatment in various processes during manufacture of the devices.
2. Description of the Related Art
FIG. 1 schematically shows a section of a conventional plasma treatment apparatus of the parallel plate type. As shown in the drawing, a semiconductor wafer 1 is placed on a lower electrode 2 to which a high-frequency voltage is applied by a high-frequency source 3. At a position above the lower electrode 2, an upper electrode 4 is disposed in parallel opposition to the lower electrode 2. The upper electrode 4 is grounded. A plurality of gas ejection holes 5 open on the lower surface of the upper electrode 4 in order to eject a processing gas into the space between the upper and lower electrodes 4 and 2 and to cause the ejected gas to diffuse in the space. The lower and upper electrodes 2 and 4 and other associated component parts are accommodated in a vacuum vessel 6.
The conventional apparatus for the plasma treatment of semiconductor devices, which has the above-described basic construction, operates in the following manner. A semiconductor wafer 1 is placed on the lower electrode 2. The interior of the vacuum vessel 6 is evacuated through an evacuation port 7 which is provided as an evacuation means on the vacuum vessel 6. When the interior of the vacuum vessel 6 has reached a predetermined degree of vacuum, processing gas is introduced through a gas introduction port 8 provided at an upper position of the upper electrode 4. The processing gas is ejected from the gas ejection holes 5 opening on the lower surface at the bottom of the upper electrode 4, and diffuses in the space between the upper and lower electrodes 4 and 2. Subsequently, a high-frequency voltage is applied to the lower electrode 2 by the high-frequency source 3, thereby generating a plasma in the space between the lower and upper electrodes 2 and 4, so that the semiconductor wafer 1 is treated with the plasma. A semiconductor device is subjected to plasma treatment during such processes as etching and ashing.
The above-described conventional plasma treatment apparatus entails the following problems. The processing gas ejected from the gas ejection holes 5 opening on the lower surface at the bottom of the upper electrode 4 diffuses in the space between the upper and lower electrodes 4 and 2, and a part of the gas diffuses outward from the space and is finally discharged through the evacuation port 7. Consequently, the amount of the gas which reaches the surface of the semiconductor wafer 1 is relatively small for the entire amount of the processing gas actually introduced through the gas introduction port 8. Thus, the semiconductor wafer 1 is processed with low efficiency. Another problem is that, since a part of the ejected processing gas diffuses outside of the space between the upper and lower electrodes 4 and 2, the gas on the surface of the semiconductor wafer 1 is unevenly distributed. This results in decreased processing efficiency and uneven treatment of various portions of the surface of the semiconductor wafer 1.